1. Technical Field:
This invention relates in general to controlling electromagnetic emissions and in particular to a planar shield with high density contacts for grounding both input and output high speed circuit electromagnetic emissions.
2. Description of Related Art:
The ever-increasing speed of modern computer processors or CPUs has given rise to increased electromagnetic interference (EMI) emissions. As a result, the need to develop better techniques and procedures for controlling EMI has also increased to keep pace with U.S. and European emission regulations.
In the prior art, high speed circuit electromagnetic emissions are typically eliminated or reduced via a direct ground connection which allows a return path for the high speed signals. The return paths are generally located close to the point of origin to reduce the length of the return paths, and to reduce the amount of radiating surface area that can release the emissions. In the prior art, radiating signals between the source and ground have been suppressed through spring clips or conductive gaskets. As long as the processors remain close to the motherboard they were attached to, EMI reductions involving spring clips were not needed.
However, with the advent of ultra high speed processors, improved EMI reduction techniques are needed. This need is compounded by the fact that the heatsinks used to cool the processors are the primary source of the CPU""s radiated energy and emissions. Since the heatsinks are typically free-floating (i.e. not attached to the system planar board), the emissions are free to radiate throughout the system and out of the system enclosure. Thus, an improved system for grounding the EMI emissions of high speed processors is needed.
A shield for grounding input and output electromagnetic emissions in a computer is formed from a rectangular plate having apertures for receiving various electrical connectors that insert into the computer. Each aperture in the plate has grounding members for engaging the connectors. The plate also has a row of spring-like wiping members along each of the four side edges. Two edges of the plate each have a single row of wiping members, and two edges of the plate have two opposed rows of wiping members. The opposed rows are interposed with each other in an alternating sequence. One of the two opposed rows forms a series of folds, and the other row forms a series of tabs.
The shield is mounted to the side edge flanges of a rectangular opening in the wall of the computer. Two of the flanges slidingly engage the single row of wiping members. The other two flanges insert into the folds and contact with both the folds and the tabs. After the shield is installed, the computer cables and connectors are inserted through the apertures and interconnected with the computer. As the cables and connectors move, the double row wiping members allow the shield to float in the computer opening while maintaining electrical grounding contact with all four of its flanges.